Here is the full list of all 20 AER - there are Memories of Old achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Find the Ancient Llamba.
Find the ancient battlefield.
Speak to all of the spirit animals.
Discover all areas of the map.
Find the statue of the fox.
Find the statue of crane.
Step into the well.
Find the statue of the deer.
Completed the game.
Complete the Monastery.
Find the dwellings of the rift cult.
Find Erin when she's gone.
Complete the Archives.
Find the chiseled stone map.
Find the giant birdshrine.
Find the Crab Island.
Complete the Eventide Sanctuary.
Find the bones of an old beast.
Get some Lambaby love.
Escape the collapsing cave.